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SESSION 3: PATHOGENESIS – EPIDEMIOLOGY AND POPULATION
GENETICS
Synopsis of microscopic and molecular studies in F.
langsethiae pathogenicity.
H. H. Divon 1 , E. Lysøe 2 , S. S. Klemsdal 2
1 Section of Mycology, Norwegian Veterinary Institute, PO Box 750, Sentrum, 0106 Oslo, Norway;
2 Department of Plant Health and Plant Protection, Bioforsk - Norwegian Institute of Agricultural and
Environmental Research, 1432 Ås, Norway
E-mail: hege.divon@vetinst.no
F. langsethiae is a common grain contaminant of small grain cereals in the Nordic
countries and the UK, and is considered the main producer of T-2 and HT-2
mycotoxins in this region. In a recently ended project we have studied, at the
micro-level, the infection process of F. langsethiae in oats, and have tried to link
the infection to molecular mechanisms by characterizing the F. langsethiae
transcriptome.
Using histology and microscopy techniques such as scanning electron
microscopy (SEM) we traced the route of initial infection of F. langsethiae on oat
grains. The colonization would typically start at the grain apex and spread
basipetally and laterally, with a clear directional growth towards the caryopsis.
Apical and ventral parts of the grain were colonized before the dorsal side. Hyphal
growth on abaxial surfaces was scanty, however clearly aided by the presence of
pollen. Heavy secretion and mucosilation was detected in the vicinity of hyphae.
At 10-14 dpi the fungus was established apically on the caryopsis surface,
growing rather profusely and developing penetration structures such as infection
hyphae and structures resembling compound appressoria.
In order to study the molecular mechanisms during plant invasion we performed
transcriptome sequencing of non-normalized cDNA libraries using 454 technology
(RNA-seq) of the fungus grown on three different media, of which two were
simulating in planta growth conditions. De novo assembly of the reads resulted in
18,742 transcriptional contigs (TCs) representing putative transcripts. Of these,
81% (15,322) were identified with a putative function based on sequence
similarity. Calculating expression levels of the TCs the main differences between
the libraries were identified. Quite conspicuously, homologs of the entire
biosynthetic pathway of depudecin, a HDAC inhibitor first identified in Alternaria
brassicicola, were among the highest expressed TCs in oat grain medium. The
data will be discussed in a biological context.
Keywords: Fusarium langsethiae, transcriptome, SEM, depudecin
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